Book Nr. 6
Critical Properties of Phi^4-Theories
and how to extract the critical properties of the theory from the resulting divergent power series.
These properties are calculated for various second-order phase transitions of three-dimensional
systems with high accuracy, in particular the critical exponents observable in experiments close to the phase transition.
Beginning with an introduction to critical phenomena, this book develops the functional-integral description
of quantum field theories, their perturbation expansions, and a method for finding recursively
all Feynman diagrams to any order in the coupling strength.
Algebraic computer programs are supplied on accompanying World Wide Web pages.
The diagrams correspond to integrals in momentum space. They are evaluated in 4-e dimensions,
where they possess pole terms in 1/e. The pole terms are collected into renormalization constants.
The theory of the renormalization group is used to find the critical scaling laws.
They contain critical exponents which are obtained from the renormalization constants
in the form of power series. These are divergent, due to factorially growing expansion coefficients.
The evaluation requires resummation procedures, which are performed in two ways:
of the specific heat of superfluid helium is shown to agree very well
with the extremely precise experimental number found in the space shuttle
orbiting the earth (whose data are displayed on the cover of the book).
The phi4-theories investigated in this book contain any number N of fields in an O(N)-symmetric interaction,
or in an interaction in which O(N)-symmetry is broken by a term of a cubic symmetry.
The crossover behavior between the different symmetries is investigated.
In addition, alternative ways of obtaining critical exponents of phi4-theories are sketched,
such as variational perturbation expansions in three rather than 4-e dimensions,
and improved ratio tests in high-temperature expansions of lattice models.
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